In mobile telephone systems, for example those known under the acronym GSM for "global system for mobile communications", the user must be reachable regardless of location, and this must be possible particularly in a dense urban environment. To this end, the tops of certain buildings are fitted with transceiver "base" stations which communicate with users either directly if they are within the range of the antenna of the base station, or indirectly via active reflector antennas or "active repeaters" which, as their name implies, reflect radio signals transmitted by the nearby base station and vice versa for user returns to the base station.
Each reflecting antenna is in fact made up of two antennas, one having its radiation pattern pointing towards the base station and the other having its radiation pattern pointing towards the user, with the two antennas being interconnected by two electrical amplification paths, one for the station-to-user direction and the other for the user-to-station direction.
Such pairs of antennas suffer from the major drawback of having directional radiation patterns to avoid the risk of oscillation, thereby restricting the user coverage zone of such an antenna and increasing the number of reflective antennas that need to be used to cover a given zone. This gives rise to ever-increasing numbers of reflective antennas on the tops of buildings, thereby leading to higher overall cost.